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SubjectRe: [PATCH] ARM: futex: fix clobbering oldval
On Thu, 2011-09-22 at 18:26 +0100, Will Deacon wrote:
> Hi,
>
> On Thu, Sep 22, 2011 at 03:53:35AM +0100, mhban wrote:
> > This patch fixes clobbering oldval bug. oldval should be preserved for next
> > compare operation.
> >
> > Change-Id: I2a63bc1bdb8de330eb9e1ac02d7da1f77e6e8c3c
> > Signed-off-by: Minho Ban <mhban@samsung.com>
>
> It would have been nice to have been CC'd on this...

Will not miss next time. Thanks.

>
> I ran LTP tests on this, so I'm surprised that this was broken (the tests
> passed). Well spotted anyway!
>
> > ---
> > arch/arm/include/asm/futex.h | 6 +++---
> > 1 files changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/arm/include/asm/futex.h b/arch/arm/include/asm/futex.h
> > index d2d733c..b0f2e8e 100644
> > --- a/arch/arm/include/asm/futex.h
> > +++ b/arch/arm/include/asm/futex.h
> > @@ -30,14 +30,14 @@
> > __asm__ __volatile__( \
> > "1: ldrex %1, [%2]\n" \
> > " " insn "\n" \
> > - "2: strex %1, %0, [%2]\n" \
> > - " teq %1, #0\n" \
> > + "2: strex r5, %0, [%2]\n" \
> > + " teq r5, #0\n" \
> > " bne 1b\n" \
> > " mov %0, #0\n" \
> > __futex_atomic_ex_table("%4") \
> > : "=&r" (ret), "=&r" (oldval) \
> > : "r" (uaddr), "r" (oparg), "Ir" (-EFAULT) \
> > - : "cc", "memory")
> > + : "r5", "cc", "memory")
>
> You shouldn't reference r5 directly here, but due to the way the futex code
> is laid out, you can't add an extra output operand without converting the
> code to use named arguments.
>
> I'll post a patch to do that.
>
> Will

I'm not familiar with gcc inline, thanks for pointing it out.

BTW, my last name is Ban not Ben.


Minho




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